In Metro Ethernet Forum, the Carrier Ethernet (CE) is longitudinally divided into three layers, and each layer has an independent OAM capability. The OAM function of an ETH service layer is independent from an upper layer application, for example, an internet protocol (IP) layer or a transmission technique of a lower layer, for example, a synchronous digital hierarchy (SDH), thereby providing ETH services by adopting different techniques. The OAM function of each layer is enhanced by one another, thereby providing desirable failure and performance management.
In IEEE 802.1ag, a maintenance domain (MD), a maintenance association (MA), an MD level, an MEP, and a maintenance intermediate point (MIP), as well as other concepts are defined. The MEP is associated with the MA, is a node on a border of the MA, and is an initiator of all OAM frames. The MEP is indicated by two parameters, that is, 1. an MAID and 2. an MEPID. The MAID is configured to indicate which MA the MEP belongs to. The MEPID is configured to indicate one MEP in one MA identified by the MAID, and one MEP has an overall uniqueness in the MA. In one word, as for a represented range, a relation of MEP MA MD exists. The MEP is divided into two types, that is, an Out-line type and an On-line type.
In Y.1731, the concept of MD is not defined, but a maintenance entity group (MEG) defined in Y.1731 is the same as the MA, an MEG Level is the same as the MD Level, and the MEP and the MIP are defined in both Y.1731 and IEEE 802.1ag.
Before working, a network level OAM needs to be configured, that is, information about the MA/MEG, MD (if needed), MD Level/MEG Level, MEP, and MIP needs to be configured for a certain concerned connection. The information about all the MEPs in the same MA/MEG needs to be configured to all the MEPs in the same MA/MEG, and then, all the MEPs configured on the MA/MEG need to periodically send a continuity check message (CCM) frame. That is to say, if one MA/MEG has n MEPs, it needs to periodically receive (n−1) CCMs, and each MEP needs to send a multicast CCM to each of the other MEPs in the same MA/MEG. If any one of the MEPs in one MA finds that it does not receive the CCM sent from any one of the other (n−1) MEPs in the current MA/MEG, the network checks a continuity failure, and corresponding measures need to be taken, for example, reporting a system failure.
A configuration time difference exists during the process of configuring the information about the MEPs, so that a mis-check of the continuity is resulted from the time difference for delivering the configuration to the MEPs. If it plans to establish 10 MEPs to be checked in a certain MA/MEG, the information about the 10 MEPs needs to be delivered to the 10 MEPs. When the information about the 10 MEPs is configured to a first MEP, the MEP may start to periodically send a CCM frame, and expect to receive 9 CCM frames from the other MEPs. Due to the time difference in the configuration process, the other 9 MEPs possibly cannot send the CCM frames since the configuration thereof is not delivered yet. In this case, the first configured MEP may generate a mis-check of the continuity. The more configured MEPs exist in the MA/MEG, the more obvious the mis-check of the continuity will be.
Under the restriction of the mechanism, the leaving of an MEP may also result in a mis-check of the continuity. The ETH OAM exists as a normal-state OAM mechanism of the ETH, and thus, once the OAM starts to work, as long as the configuration is not cancelled, the OAM needs to work un-intermittently. If a certain MEP in the MA/MEG leaves due to a certain reason, the other MEPs consider the leaving as a failure. Therefore, the mis-check of the continuity is resulted.